boolean SIDESTICK = false;
boolean[][] isTaken;

void setup() {
  size(512, 512);
  background(0);
  isTaken = new boolean[width][height];
  isTaken[width/2][height/2] = true;
}

void draw() {
  int x = floor(random(width));
  int y = floor(random(height));
  if (isTaken[x][y]) {
    return;
  }
  while (true) {
    int xp = x + floor(random(-1, 2));
    int yp = y + floor(random(-1, 2));
    boolean iscontained = (
      0 <= xp && xp < width  &&
      0 <= yp && yp < height
      );
    if (iscontained && !isTaken[xp][yp]) {
      x = xp;
      y = yp;
      continue;
    } else {
      if (SIDESTICK || (iscontained && isTaken[xp][yp])) {
        isTaken[x][y] = true;
        set(x, y, #FFFFFF);
      }
      break;
    }
  }
  if (frameCount > width * height) {
    noLoop();
  }
}